It is well-known in the art when a certain kind of dye is added to an silver halide emulsion(herein after referred to as "silver halide emulsion" or, simply "emulsion"), sensitivity wavelength region of the emulsion is expanded and optical sensitivity is increased.
As the dye used for this purpose, a lot of compounds are known in the art, and, for example, variety of dyes such as hemicyanine dyes, cyanine dyes, merocyanine dyes and xanthene dyes, which are disclosed on pages 194 to 234 of "The Theory of the Photographic process" 4th edition, written by T. H. James published by Mcmilan Ltd. in 1977 and on pages 441 et seq. in "The Chemistry of Heterocyclic Compounds", vol. 30, written by D. M. Starmer, published by John Wiley & Sons, New York, in 1977, are known.
It is necessary for these optical sensitizing dyes not only to expand sensitive wavelength region of the silver halide emulsion but also to satisfy the following conditions.
(1) Optical sensitizing region is appropriate. PA1 (2) Optical sensitizing efficiency is high. PA1 (3) There is no advertent interaction between other photographic additives such as a stabilizer, an anti-foggant, a coating aid, a high boiling point solvent, etc. PA1 (4) They do not have advertent effects on the shape of the characteristic curve, such as occurrence of fog or fluctuation of gamma, etc. PA1 (5) When a silver halide light-sensitive material containing the dye is stored, especially under high temperature and high humidity conditions, they do not cause changes in the photographic properties such as occurrence of fog. PA1 (6) The added dye does not diffuse into a different layer having different optical sensitivity and causes color stain there. PA1 (7) After the photographic material undergoes photographic process, such as development, fixing, rinsing, etc., the dye is sufficiently removed from the system and does not cause color contamination. PA1 n represents an integer of one or two and n.sub.2, n.sub.3 and n.sub.4 independently represent an integer of zero, one or two; PA1 R.sub.1 and R.sub.2 independently represent an aliphatic group or an aromatic group, provided that they may be either same or different; PA1 X represents an oxygen atom or an alkyl-substituted nitrogen atom; PA1 L represents a hydrogen atom or an alkyl group; PA1 A represents a counter ion which is necessary to neutralize the ion charge of the molecule and n.sub.5 represents zero or one.
However, those sensitizing dyes known in the art do not satisfy all these conditions.
Incidentally, it is known in the art that the human eye has its highest visual sensitivity to green light and, therefore, subtle balance in the green-light has a great effect on the color hue. Therefore, is demanded that a silver halide light-sensitive color photographic material has sufficient sensitivity in the green-light region, that it has appropriate spectral sensitivity and that the dye can be removed sufficiently after processing.
And, in the light-sensitive materials for shooting, it is understood to be appropriate that spectral sensitivity of the green light-sensitive layer is in the wavelength region between 500 to 600 nm and the weighted average of the optical sensitivity maximum resides approximately about 540 nm.
That is to say, in order for the realization of the appropriate spectral sensitivity distribution, it is necessary for the wavelength region between 500 and 540 nm to be spectrally sensitized satisfactorily as well as in the region of longer wavelength.
Up to today, a lot of patents have been disclosed and as those in which a single kind of dye is used, for example, oxacarbocyanine dyes disclosed in U.S. Pat. Nos. 2,072,908, 2,647,053; British Patent No. 1,012825; benzimidazolocarbocyanine dyes disclosed in Japanese patent Publication Nos. 38-7828(1963), 43-14497(1968; British Patent No. 815,172; U.S. Pat. Nos. 2,778,823, 2,7639,149, 2,912,329 and 3,656,959; and oxathiacarbocyanine dyes disclosed in British Patent No. 1,012825 are known.
Further, techniques of hyper sensitization, in which an oxacarbocyanine dye is employed together with different types of dye, are disclosed in, for example, Japanese Patent Publication Nos. 43-4936(1968), 43-22884(1968), 44-32753(1969), 46-11627(1971), 48-25652(1973), 57-14834(1982) and Japanese Patent O.P.I. Publication No. 3-48235(1991).
However, with these dyes, although green-sensitivity is enhanced, good color reproduction property may not be obtainable as the spectral sensitivity region shifts to longer wavelength region.
As the sensitizing dyes used for spectrally sensitizing the wavelength region shorter than 550 rim, for example, benzimidazoloxacarbocyanine dyes disclosed in Japanese Patent Publication No. 44-14030(1969) and Japanese Patent O.P.I. Publication No. 51-31228(1976); cyanine dyes disclosed in U.S. Pat. Nos. 2,072,908 and 2,231,658; and dimethinemerocyanine dyes disclosed in U.S. Pat. Nos. 2,493,748, 2,5198,001 and 3,480,439 are known. However, when these dyes are used singly, an emulsion having enhanced spectral sensitivity in the shorter green wavelength region and, particularly a photographic emulsion having high sensitivity at the wavelength region of 540 nm or shorter can hardly be obtainable, and there is a problem that, upon attempt to enhance sensitization, fog tends to be caused easily and storage preservation property tends to be deteriorated. Still further, with the use of oxacarbocyanine dyes disclosed in, for example, U.S. Pat. Nos. 2,521705, 2,521959 and 2,647,054, which have their sensitivity maxima in the wavelength region between 530 and 540 run, there are, again defects that attainable sensitivity is relatively low and that remarkable color staining due to residual dyes takes place.
Oxacarbocyanine dyes having a sulfoalkyl group as a substituent on a nitrogen position of its molecular structure, disclosed in Japanese Patent O.P.I. Publication No. 63-163843(1988) and oxacarbocyanine dyes having a bulky substituent, as disclosed in Japanese Patent O.P.I. Publication No. 63-163843(1988) can, in comparison with the carbocyanine dyes known to date, shift the spectral sensitivity maxima towards shorter wavelength side and exert improvement in the photographic properties, however, spectral sensitivity in the wavelength region shorter than 540 nm is insufficient and, therefore, further improvement in this respect has been demanded.
As for dyes which have a fluorine atom as a substituent, symmetric carbocyanines having a monofluorine substituent or a trifluoromethyl-substituent have already been known in Japanese Patent O.P.I. Publication No. 48-76525(1973). However, although this type of dye has an effect of shifting its absorption maximum towards shorter wavelength region than 540 nm, spectral sensitivity is insufficient and, still further, asymmetrical oxacarbocyanine dyes have been known in Japanese Patent O.P.I. Publication No. 63-259554(1988),this type of dye has a defect that due to the presence of a methoxy group maximum spectral sensitivity region becomes in the wavelength region longer than 540 nm.
On the other hand, since the total processing time has been shortened and elimination of washing or rinsing or recycling of the processing solutions has become popular, the dyes tend to remain more easily and, as a result, a new problem of devaluation of the light-sensitive materials arises and, thus, improvement in the pollution by the residual dye has become one of the important items for improvement.